Sunday, July 26, 2015

The Next Maunder Minimum Will Not Freeze Your A**

Crane Beach, MA (Aug 25, 2007)

For most Bostonians, Crane beach is the place to cool off during hot summer days, taking advantage of the cool waters of the Atlantic ocean, just a short drive from town. During this time, the sandy expanse is a temple for the worshippers of the Sun, and its warming rays. I was thinking about this as I remembered a flurry of articles that appeared on the tabloids a couple of weeks ago, making apocalyptic predictions about how the Sun is on the verge of triggering a new ice age. This impending cataclysm will supposedly nullify global warming, and herald years of freezing winters followed by the absence of summer. As expected, these articles were immediately picked up by the usual climate change deniers communities. But is this really true? Are we really headed towards a new ice age?

Bi-color Crane beach

The last glacial period (ice age) lasted for over 100,000 years, and ended about 12,000 years ago. During that period the polar ice sheet reached its maximum extension, covering large areas of northern Europe, Asia and America. That was the time when the mammoths were roaming the frozen steppes of Siberia. Most of humanity lived at the edge of the ice, at more temperate latitudes, while only our cousins the Neanderthals were well adapted to the colder central European climate. This was just the last of a long succession of glacial periods in the last 2.6 million years, triggered by small changes in the orientation of Earth's orbit, with a periodic pattern called Milankovitch cycle. If we ignore the effect of anthropogenic climate change (which is instead warming the planet), we are indeed directed towards a phase of the next Milankovitch cycle that will lead to a new glaciation: this will not happen, however, for the next 50,000 years.

The ice age mentioned in last week news, however, has nothing to do with the Milankovitch cycle. It refers instead to the little ice age that hit Europe 400 years ago. This time was characterized by bitter winters in northern Europe, and is roughly coincident with a period of low solar activity, which is called Maunder Minimum. Discovered by Annie and Walter Maunder by analyzing historical counts of sunspots, the Maunder Minimum stands out as a period between 1672 and 1699 during which the Sun was almost completely devoid of sunspots. Since sunspots are the consequence of the changing magnetic activity of the Sun, counting the sunspots is a good proxy to estimate the overall activity of the Sun, with no-sunspots indicating a very quiet Sun. During the Maunder Minimum, the Sun was at its quietest of all recorded history. Why that happened is still a mystery, since there is no current physical theory capable to predict the long term ebbs and flows of the solar cycle, or tell us if and when a new minimum will occur. It is in this context that a new study announced at a meeting of the Royal Astronomical Society has triggered the media storm related to an impending new age. The authors of this study claim to have developed a complex model of solar activity capable to predict the occurrence of the next Maunder minimum, that will start in the decade between 2030 and 2040. This was enough to trigger the media storm about an imminent new ice age, that will balance the effects of anthropogenic climate change, and plunge the world into a deep freeze.

Ice age at Crane beach

The reality, unfortunately, is not so convenient. Despite the coincidence in time between the Maunder Minimum and the little ice age, there is little scientific evidence that the two phenomena are related. During the little ice age the global climate didn't change very much, with only northern Europe (and Greenland) experiencing colder than usual winters. Summers temperatures were however normal. Some line of evidence point towards the cold winters being caused not by the low activity of the Sun, but rather by concomitant massive volcanic eruptions in Indonesia and Vanuatu, releasing vast amount of ashes and sulfuric acid particles in the atmosphere, blocking the Sun and cooling the Earth. Despite the lack of evidence, the Maunder Minimum is still often mentioned as a possible cause for the little ice age in Europe. That's why, even though the original press release doesn't make any claim about an impending ice age, the press and the climate-change denier community jumped on chance of minimizing the impact of human activity on the climate, by placing the Sun in the driver's seat. But so is not: even if a little ice age could be caused by an imminent Maunder Minimum, the effect on the climate would be minuscule, dwarfed by the much larger increase caused by the greenhouse gases that we recklessly pump in the atmosphere. We unfortunately cannot count on whimsical ice ages to save us from our own foolishness.

[Edit: an earlier version of this post mentioned that the research presented at the Royal Astronomical Society meeting was not peer review. There is in fact a 2014 paper that present the model described in the press release. The research makes predictions for the near future solar activity, but does not address in any way its effect on climate.]